W10-11: Sedimentary Rocks

Knowt for W10-11 exam focused on Sedimentary Rocks

Sedimentary Facies

Bodies of sediment that are recognizably distinct from adjacent sediments. Individual depositional environments produce bodies of rock with specific characteristics (composition, texture, structures, bedding, fossils)

Depositional Environment

A specific type of place in which sediments are deposited, such as a floodplain, beach face, or sand dune. Each place produces a sedimentary facies characteristic of that place.

Facies Assemblage

A genetic grouping of facies that correlates with a particular depositional system

Depositional System

A set of genetically and geographically related depositional environments, e.g., the below storm-wave-base, between storm-wave- and fair-weather-wave-base, above fair-weather-wave-base, and shore face environments that characterize beaches

Depositional Systems Tract

All of the depositional systems present in a given area at a given time in Earth’s history

Walther’s Law of Facies

A vertical sequence of facies is the product of a series of laterally-adjacent depositional environments

Progradation

Seaward outbuilding of successive strata; that is, stacking strata such that a depositional system in an overlying layer lies seaward of the equivalent system in the underlying layer (sediment supply > accommodation space)

Aggradation

Vertical stacking of successive strata; that is, stacking strata such that a depositional system in an overlying layer lies directly above the equivalent system in the underlying layer (Sediment supply = accommodation space)

Retrogradation

Landward migration of successive strata; that is, stacking strata such that a depositional system in an overlying layer lies landward of the equivalent system in the underlying layer (sediment supply < accommodation space)

Transgression

A geologic event caused by a relative rise in sea level that results in retrogradational stacking of strata

Regression

A geologic event caused by a relative fall in sea level that results in progradational (seaward) stacking of strata

Sequence Stratigraphy

An area of stratigraphy that describes sedimentary deposits based on their stacking patterns and interprets them in terms of variations in sediment supply and in the rate of change of accommodation space.

Upper Plane-Bedding

Parallel laminations that indicate rapid flow

Cross-bedding

Laminations at an angle to bedding that indicate intermediate flow

Ripples

Small dune-forms that indicate low flow

Hummocky-bedding

Small piles of sediment surrounded by depressions. These form below fair weather wave base and above storm wave base.

Parallel Laminations

Parallel bedding formed by variations in the sedimentation rate of fine-grained sedimentM

Mud Cracks

Desiccation cracks in clay-rich sediments that indicate subaerial conditions and transitions between wet and dry periods (as found in desert climates)

Bioturbation

Disruptions in and on beds (e.g. burrows) caused by moving (feeding) organisms

Massive Bedding

Homogenous beds with no sediment sorting or laminations

Turbidite Sequence

Point Bar Sequence

Beach Sequence